The present invention relates to an inverting device for inverting a pair of substrates by clamping the pair of substrate with a pair of clamping members, and to a method for manufacturing a liquid crystal display panel using the inverting device.
Within the field of display devices, liquid crystal display devices can have characteristics of thin profile and low power consumption.
The liquid crystal display device includes a liquid crystal display panel (hereinafter referred to as a display panel) and a backlight unit. In the case wherein the backlight unit is an edge light type, the backlight unit is configured such that it includes a light-guiding plate and the light emitted from a light source enters the light-guiding plate though a side surface and is radiated from a main surface, irradiating a back surface of the display panel.
The display panel includes a color filter substrate (hereinafter referred to as CF substrate) having a plurality of color filters, an active matrix substrate (hereinafter referred to as TFT substrate) having a plurality of thin film transistors (hereinafter referred to as TFT) as switching elements which is arranged to face the CF substrate and, a liquid crystal layer provided between the CF substrate and the TFT substrate, which are disposed to face each other with a predetermined gap maintained by a spacer, as a display medium layer.
With regard to the methods for manufacturing a display panel, reference can be made to, for example, JP 2006-349913 A. It describes firstly applying a sealing material to the inside of a circumferential part of each unit of a CF substrate, and then dropping a liquid crystal material inside the sealing material on the substrate in the form of a dot. The sealing material is ultraviolet curable and heat curable.
Then, the CF substrate and the TFT substrate are bonded together under vacuum atmosphere (hereinafter a pair of bonded substrates is referred to as a bonded substrate) with the CF substrate facing up. With regard to examples of an inverting device for a CF substrate, JP 2003-233052 A discloses a device configured such that after a liquid crystal material has been dropped on a TFT substrate and a sealing material has been applied to a CF substrate, the CF substrate is inverted so that the coated surface is in the bottom position, and then the CF substrate is bonded to the TFT substrate.
Next, the bonded substrate is inverted so that the TFT substrate is on the top, and the sealing material is pre-cured by irradiating ultraviolet light towards the TFT substrate of the bonded substrate. In the configuration in which a black matrix of a CF substrate and a sealing material are provided so as to overlap with each other for attaining a narrow frame, it is necessary to invert a bonded substrate so that the TFT substrate is on the top and the ultraviolet light can be irradiated through the TFT substrate.
After the irradiation of ultraviolet light, the bonded substrate is inverted so that the CF substrate is on the top, and the bonded substrate is heated at 130° C. for about 70 minutes for main curing of the sealing material. The bonded substrate is inverted because the bonded substrate should be transported with the CF substrate up in order to protect the CF substrate, which will be used for the front surface of the display panel, from being damaged.
Finally, the display panel is divided into units.
As described above, the bonded substrate is inverted using an inverting device. As inverting device, devices provided with a motor to invert a bonded substrate while clamping a bonded substrate by a plurality of pairs of clamping members can be used.
The clamping members are provided with a covering layer made of an inexpensive resin, such as polyolefin, on a surface of a core portion which is made of a metal.
The pairs of clamping members clamp a bonded substrate in the state where each of the covering layers of the clamping members contacts with the surfaces of the bonded substrate, and thus when the pair of clamping members is pressed to the bonded substrate and the bonded substrate is inverted, a substrate contacting surface of the clamping members tends to slightly slide in relation to the substrate surface, producing wear debris. The wear debris is made of, for example, polyethylene, polypropylene and the like. A melting point of polyethylene is 100 to 120° C. and a melting point of polypropylene is 120 to 130° C. Since those melting points are lower than the above-mentioned heat-curing temperature of 130° C., the wear debris will be melted on the surface of the display panel during heat-curing.
After cooling the bonded substrate, the melted wear debris is fixed to the surface of the display panel. The fixed wear debris cannot be completely removed by washing which is carried out when the bonded substrate is divided into the units or washing which is carried out after the circuit board mounting, and further, they are hardly recognized visually in, for example, a quality inspection process such as a visual inspection of the substrate before the polarizing plate is attached to. The wear debris can be visually recognized as a foreign substance only after the polarizing plates are attached to both outer surfaces of the bonded substrate, and a product will then be recognized faulty.